Gem with brilliant cut

ABSTRACT

Brilliant-cut gemstone, wherein the crown angle (α) is between 32.8° and 33.0°.

To increase the brilliance of a faceted cut gemstone, diverse types ofcuts have been developed over time, which, on the one hand, differ bythe number of facets and, on the other hand, by the mutual geometricrelationships of the facet positions.

The so-called brilliant cut has been found to be especially esthetic inparticular for diamonds since this cut critically impacts the so-called“fire” of the diamond, which fire is based on numerous internal lightreflections. These light reflections occur at the individual facetswhich have special angular relations with one another characterizing theparticular cut. Consequently, the cut of a gemstone, especially that ofa diamond, is decisive for the generated fire.

Further parameters characteristic of the esthetics of a gemstone, thatare dependent on the particular cut, are the scintillation describingthe sparkle of a moved gemstone and the brilliance describing thebrightness and the contrast of the light exiting from a gemstone. Adiamond with a brilliant cut is generally also referred to as abrilliant.

A gemstone with brilliant cut includes a crown, also referred to as thetop part, with at least 32 facets and a table, as well as a pavilion,also referred to as the bottom part, with at least 24 facets. The endopposite the table of the gemstone can be formed as a point or as arounded-off point in the form of a so-called culet. Between top andbottom part is disposed the so-called rondiste or girdle. The gemstoneis cut symmetrically.

The invention addresses the problem of further improving the estheticimpression of a gemstone with brilliant cut, for example providingincreased luminous efficiency or increased luminance or brightness.

This is resolved in a gemstone with the features of claim 1.

Thereby that the gemstone has a brilliant cut in which the crown angleis between 32.8° and 33°, an especially high luminous efficiency wasunexpectedly obtained, whereby the fire, the scintillation and thebrilliance of the gemstone are being brought out especially well.

The crown angle is that angle which, in a side view of the gemstone, isformed between the lateral boundary line of the crown and the girdleplane, wherein this boundary line results by orthogonal projection of acrown facet onto a plane containing the longitudinal axis of thegemstone.

The girdle plane is that plane which is located parallel to the tableand in which the gemstone has its greatest cross-sectional dimension.The girdle plane is oriented perpendicularly to the longitudinaldirection of the gemstone.

To measure the luminous efficiency or brightness of the gemstone, whichefficiency corresponds to a reflected light fraction, measurements arecarried out using an illumination arrangement and measuringspecifications developed by the Gemological Institute of America (GIA).The corresponding measuring specifications are found in the magazine“Gems & Gemology”, Fall 2004, pp. 202-228, in which, in particular onpage 219, a measuring arrangement for measuring the brightness of agemstone is depicted. Instead of an actual measurement, the measurementcan also be computationally simulated based on the geometry of thegemstone. The measurement or the results of the simulation yield valuesfor several characteristic light- or radiation-specific parameters ofthe gemstone, in particular brightness and/or luminous efficiency.

The gemstone located in the center of the base circle is illuminatedusing a hemispherical illumination arrangement with directed irradiationnormal to the surface. The illumination arrangement generates a Lambertbeam distribution with sufficiently large sectional angle such thatlateral facets of the gemstone are also illuminated. The quantity oflight reflected by the gemstone represents a mean value over nearly allpossible illumination configurations and consequently provides aquantitative measure of the luminous efficiency or the brightness of thegemstone. The higher the fraction of the reflected or backscatteredlight, the higher is the light efficiency and the brightness and thebetter is the reflection behavior of the gemstone, which is accompaniedby esthetic perceptions of higher value.

To measure the reflected or backscattered light serves a photo-currentdetector at a very large distance, relative to the dimensions of thegemstone, with a narrow measuring field.

Further advantageous embodiments of the invention are defined in thedependent claims.

In a preferred embodiment the pavilion angle is between 41.7° and 41.9°.

The pavilion angle is that angle formed, in a side view of the gemstone,between the lateral boundary line of the pavilion and the girdle plane,wherein this boundary line is obtained by orthogonal projection of apavilion facet onto a plane including the longitudinal axis of thegemstone.

Although the gemstone according to the invention can be produced of anydesired natural or synthetic precious or semiprecious stone, a gemstoneof glass or synthetic material with the brilliant cut according to theinvention is also feasible.

It was herein unexpectedly found that an especially high luminousefficiency is realizable at a crown angle between 32.8° and 33° and/orat a pavilion angle between 41.7° and 41.9° if the gemstone is comprisedat least to a large extent, preferably entirely, of cubic zirconia.

The pavilion, also known as bottom part, has at least 24 pavilionfacets, which come together at the end opposite the table in the form ofa point or a culet. In one embodiment eight pavilion facets have a pointlocated in the direction toward the girdle, while 16 pavilion facetshave a broadside bordering on the girdle. The end located opposite thebroadside of these pavilion facets forms a point and is directed awayfrom the girdle. The orthogonal projection of the last-cited pavilionfacets yields the pavilion angle.

In one embodiment of the invention the angle between the girdle planeand those pavilion facets that have a point bordering on the girdle orlocated in the direction toward the girdle, is between 41.7° and 41.9°.Additionally or alternatively, it can be provided that the angle betweenthe girdle plane and those pavilion facets that have a broadsidebordering on the girdle is between 42.8° and 43.0°.

The crown of the gemstone, also known as the top part, includes a tablewhich is bordered by eight crown facets with one broadside each. In oneembodiment of the invention these crown facets form with the girdleplane an angle between 20.2° and 20.4°.

The crown includes furthermore sixteen crown facets which have a pointbordering on the girdle. In one embodiment of the invention these crownfacets form with the girdle plane an angle between 39.3° and 39.5°.

The crown includes furthermore eight additional crown facets, each ofwhich borders with a broadside on the girdle. In one embodiment of theinvention the angle between these crown facets and the girdle plane isbetween 32.8° and 33.0°. The orthogonal projection of the last citedcrown facets forms the crown angle.

Further details and advantages of the present invention will beexplained in further detail in conjunction with the description of thefigures with reference to the drawing. Therein depict:

FIG. 1 a to 1 c a side view, a top view as well as a view from belowonto a gemstone according to the invention,

FIG. 2 a schematic representation regarding the definition of the crownangle and of the pavilion angle,

FIGS. 3 a and 3 b a comparison of a gemstone of prior art with agemstone according to the invention using a schematic depiction of pathsof rays,

FIG. 4 a schematic depiction of the measuring arrangement for measuringthe luminous efficiency or brightness.

FIG. 1 a shows a gemstone 1 according to the invention in a side view.Evident is the girdle 4, which separates the crown 2, also referred toas the top part, from the pavilion 3, also referred to as the bottompart. The girdle 4 is the region of the greatest cross-sectionaldimension of the gemstone 1. Schematically shown is furthermore the axisof symmetry of the gemstone in the longitudinal direction whichcorresponds to the longitudinal axis of the gemstone.

The pavilion 3 has two types of pavilion facets 8, 9. Herein sixteenpavilion facets 9 include a broadside with which these facets border onthe girdle 4. At the opposite end the pavilion facets 9 come together inthe form of a point in the direction toward the culet 6. The remainingpavilion facets 8 include a point, each of which borders on the girdle4.

The crown 2 comprises 32 facets 10, 11, 12 as well as a table 5 orientedparallel to the girdle plane 7.

Sixteen crown facets 12 border with one broadside on the girdle 4 andhave a point directed in the direction of the table 5. Eight furthercrown facets 10 border with one broadside each on the table 5. Theremaining eight crown facets 11 have each a total of four points, ofwhich one point borders on the table 5, while another point borders onthe girdle 4.

Evident is also the lateral boundary line 16 of crown 2, which is formedas the orthogonal projection of the crown facets 12, and the lateralboundary line 17 of the pavilion 3 formed as the orthogonal projectionof the pavilion facets 9.

In one embodiment example of the invention the gemstone 1 is comprisedof cubic zirconia and has a crown angle α between the lateral boundaryline 16 and the girdle plane 7 of 32.9° and a pavilion angle β betweenthe lateral boundary line 17 and the girdle plane 7 of 41.8°. The anglebetween the girdle plane 7 and the crown facets 12, which border withtheir broadside on the girdle 4, is 39.4°. The angle between the girdleplane 7 and those crown facets 10 which border with their broadside onthe table 5, is 20.3°. The angle between the girdle plane 7 and theremaining crown facets 11 is 32.9°. The angle between the girdle plane 7and the pavilion facets 9, which border with their broadside on thegirdle 4, is 42.9°. The angle between the girdle plane 7 and theremaining pavilion facets 8 is 41.8°.

FIG. 1 b depicts a top view onto the crown 2 of the gemstone 1. Theschematically shown rectangular coordinates on table 5 make evident thesymmetry of the gemstone 1.

FIG. 1 c depicts a view from below onto the pavilion 3 of the gemstone1. On the culet 6 formed by the pavilion facets 8 bordering on oneanother, is symbolically depicted a further rectangular coordinatesystem to illustrate the symmetry of the gemstone 1.

FIG. 2 shows a schematic depiction to explain the crown angle α, whichis formed between the girdle plane 7 and the lateral boundary line 16 ofcrown 2, while the pavilion angle β is formed between the lateralboundary line 17 of pavilion 3 and the girdle plane 7.

FIG. 3 a shows a gemstone 1′ with brilliant cut according to prior art.The light rays 13 entering the gemstone are only partially reflected onpavilion 3′ due to the angles at which the different pavilion facets arecut, in particular due to the crown angle and to the pavilion angle. Afraction of the rays exits from the pavilion 3′ in the form of refractedrays 14. The ratio of the light rays 15 exiting from the crown 2′ to thelight rays 13 entering into the crown 2′ defines the luminousefficiency.

FIG. 3 b shows the same depiction but of a gemstone 1 according to theinvention. The luminous efficiency is markedly improved due to thespecific geometric configurations of the different facets and of thecrown angle aα and of the pavilion angle β3, since the majority of therays is totally internally reflected in the region of pavilion 3 suchthat nearly the entire fraction of light rays 13 entering the crown 2,after possibly multiple reflections, is reflected back to the viewer inthe form of light rays 15 exiting from the crown 2.

FIG. 4 shows in schematic view a measuring arrangement for measuring thebrightness or luminous efficiency of a gemstone employing the measuringspecifications of the cited article in the magazine “Gems & Gemology”.Using a hemispherical illumination arrangement 16 a gemstone 1, locatedin the center of a base circle 17 of the hemisphere 16, is illuminatedby light rays 18 such that the crown 2 of the gemstone 1 is irradiatedwith white diffuse light, wherein the light beams, except for a shieldedregion 19, impinge hemispherically onto the gemstone 1 and are reflectedat it. Except for a recess for the gemstone 1, the base circle 17 isshielded such that no light impinges on the gemstone 1 from below thebase circle 17. Also shielded is a region 19 of the hemisphere 16, whichis precisely opposite the gemstone 1 and has an aperture angle α of 46°.From this region there is also no light reaching the gemstone 1. Theregion 19 includes a recess 20 with an angle of aperture β of 3°. Thisrecess 20 serves as the measuring field for a detector. Consequently,above the recess 20 a detector measuring a photo current can bedisposed. Instead, the particular light-specific values, such as forexample the brightness, can be calculated in the region of this recess20 in a computer simulation.

The quantity of light reflected by the gemstone 1 represents a meanvalue over nearly all possible illumination configurations andconsequently yields a quantitative measure of the luminous efficiency orthe brightness of the gemstone 1. The reflections occur herein ondistinct facets such that light is directly reflected back to the recessupon the first impingement onto the gemstone, however also after severalinternal reflections.

1. Brilliant-cut gemstone, characterized in that the crown angle (″) isbetween 32.8E and 33.0E.
 2. Gemstone as claimed in claim 1,characterized in that the pavilion angle ($) is between 41.7E and 41.9E.3. Gemstone as claimed in claim 1, characterized in that the gemstone(1) is comprised at least to a large part, preferably entirely, of cubiczirconia.
 4. Gemstone as claimed in claim 1, characterized in that theangle between the girdle plane (7) and those pavilion facets (8), whichhave a point disposed in the direction toward the girdle (4), is between41.7E and 41.9E, and/or the angle between the girdle plane (7) and thosepavilion facets (9) which border with a broadside on the girdle (4) isbetween 42.8E and 43.0E.
 5. Gemstone as claimed in claim 1,characterized in that the angle between the girdle plane (7) and thosecrown facets (10), which border with a broadside on the table (5), isbetween 20.2E and 20.4E and/or the angle between the girdle plane (7)and those crown facets (11) which have a point bordering on the girdle(4) is between 32.8E and 33.0E and/or the angle between the girdle plane(7) and those crown facets (12) which border with a broadside on thegirdle (4) is between 39.3E and 39.5E.
 6. Gemstone as claimed in claim2, characterized in that the gemstone (1) is comprised at least to alarge part, preferably entirely, of cubic zirconia.
 7. Gemstone asclaimed in claim 2, characterized in that the angle between the girdleplane (7) and those pavilion facets (8), which have a point disposed inthe direction toward the girdle (4), is between 41.7E and 41.9E, and/orthe angle between the girdle plane (7) and those pavilion facets (9)which border with a broadside on the girdle (4) is between 42.8E and43.0E.
 8. Gemstone as claimed in claim 3, characterized in that theangle between the girdle plane (7) and those pavilion facets (8), whichhave a point disposed in the direction toward the girdle (4), is between41.7E and 41.9E, and/or the angle between the girdle plane (7) and thosepavilion facets (9) which border with a broadside on the girdle (4) isbetween 42.8E and 43.0E.
 9. Gemstone as claimed in claim 2,characterized in that the angle between the girdle plane (7) and thosecrown facets (10), which border with a broadside on the table (5), isbetween 20.2E and 20.4E and/or the angle between the girdle plane (7)and those crown facets (11) which have a point bordering on the girdle(4) is between 32.8E and 33.0E and/or the angle between the girdle plane(7) and those crown facets (12) which border with a broadside on thegirdle (4) is between 39.3E and 39.5E.
 10. Gemstone as claimed in claim3, characterized in that the angle between the girdle plane (7) andthose crown facets (10), which border with a broadside on the table (5),is between 20.2E and 20.4E and/or the angle between the girdle plane (7)and those crown facets (11) which have a point bordering on the girdle(4) is between 32.8E and 33.0E and/or the angle between the girdle plane(7) and those crown facets (12) which border with a broadside on thegirdle (4) is between 39.3E and 39.5E.
 11. Gemstone as claimed in claim4, characterized in that the angle between the girdle plane (7) andthose crown facets (10), which border with a broadside on the table (5),is between 20.2E and 20.4E and/or the angle between the girdle plane (7)and those crown facets (11) which have a point bordering on the girdle(4) is between 32.8E and 33.0E and/or the angle between the girdle plane(7) and those crown facets (12) which border with a broadside on thegirdle (4) is between 39.3E and 39.5E.
 12. Gemstone as claimed in claim6, characterized in that the angle between the girdle plane (7) andthose pavilion facets (8), which have a point disposed in the directiontoward the girdle (4), is between 41.7E and 41.9E, and/or the anglebetween the girdle plane (7) and those pavilion facets (9) which borderwith a broadside on the girdle (4) is between 42.8E and 43.0E. 13.Gemstone as claimed in claim 7, characterized in that the angle betweenthe girdle plane (7) and those crown facets (10), which border with abroadside on the table (5), is between 20.2E and 20.4E and/or the anglebetween the girdle plane (7) and those crown facets (11) which have apoint bordering on the girdle (4) is between 32.8E and 33.0E and/or theangle between the girdle plane (7) and those crown facets (12) whichborder with a broadside on the girdle (4) is between 39.3E and 39.5E.14. Gemstone as claimed in claim 8, characterized in that the anglebetween the girdle plane (7) and those crown facets (10), which borderwith a broadside on the table (5), is between 20.2E and 20.4E and/or theangle between the girdle plane (7) and those crown facets (11) whichhave a point bordering on the girdle (4) is between 32.8E and 33.0Eand/or the angle between the girdle plane (7) and those crown facets(12) which border with a broadside on the girdle (4) is between 39.3Eand 39.5E.